EP2683503B1 - Method and device for angle-precise edging or bending of sheet metal plates - Google Patents

Description

The present invention relates to a method for bending or bending sheet metal with precise angles, with the features of claim 1. The invention also relates to a device for carrying out a method for bending or bending sheet metal with precise angle.

The production of exact, predetermined bending angles when bending or bending sheet metal is a relatively complex process, the path to be set by a bending punch of a folding machine to produce a certain angle both from the material of the sheet, the sheet thickness and from the relative position of the bending direction with respect to the rolling direction of the Sheet depends. In addition, in a bending process, the bending-deformed workpiece springs back when the bending deformation ceases or ends by relieving the workpiece of the bending force due to the elasticity of the material, the bending angle also changing. Depending on how large the deviation of the bending angle actually reached from the specified bending angle, a correction bending must be carried out. For this purpose, the bending angle actually achieved is measured and the sheet metal part is then bent again with correction parameters according to the difference between the angle already achieved and the desired angle. The angle measurement to be carried out is a complex process that can be carried out in different ways.

In the case of a method that requires little equipment, but is all the more time-consuming, the sheet metal part is removed from the bending device and measured using an angle measurer. The sheet metal part is then put back into the machine and reworked according to the difference between the measured angle and the specified angle.

The DE 100 09 074 A1 discloses an object according to the preamble of claim 12. In the DE 100 09 074 A1 describes a method for free or swivel bending of a workpiece and a device for determining the position of a workpiece leg during bending. In this case, the resulting bending angle is determined with the aid of an optical measuring beam, which is directed onto the workpiece leg (s) to be checked with regard to the angular position and is designed as a light plane or light beam in such a way that a light line or light path is generated on the workpiece or workpiece leg. The position of the impact point on the workpiece leg, which is dependent on the bending angle, is recorded by means of a camera and the change in angle of the position of the impact point can be determined.

From the DE 10 2006 050 687 B4 is known a method for measuring and / or correcting the workpiece shape after forming by bending, wherein a first section of the workpiece is firmly clamped, a second section is bent around a bending edge and a straight part of the second section following the bending after the bending process with respect to its location to the first section is measured. In the area of the straight part of the second section of the workpiece, at least two measuring points are determined at different distances from the bending edge, the connecting straight line of which gives the actual bending angle, the difference between the measured actual bending angle and a predetermined bending angle are used to calculate the deformation path for a subsequent final or iterative bending process.

In the DE 10 2007 056 827 B3 describes a controller for a bending machine, which has interfaces to one or more laser-assisted bending angle measuring devices and can communicate with one or more force measuring devices. The controller can use construction data and / or workpiece data for the parts to be bent to calculate parameters for controlling the bending machine, setpoints for the angles of the parts to be bent and position data for one or more laser-assisted bending angle measuring devices. Using actual values from one or more laser-assisted bending angle measuring devices and from one or more force measuring devices, the controller can correct the parameters for controlling the bending machine until there is a match between the target values and the actual values. This controller is preferably part of a fully automatic bending system.

All of the above-mentioned methods have the disadvantage that, at least at the beginning of a new production series, the bending angles have to be checked after each bending or bending, and one or more corrective bends may have to be carried out. In particular if sheet metal with fluctuating quality is used, frequent control measurements must also be carried out during the production series.

In the case of a semi-automatic machine, the angle is determined by removing the workpiece from the machine and then measuring the angle generated by the machine operator using an angle meter. Should the difference between the generated angle and the specified angle outside the specified tolerance, the workpiece is inserted into the machine again and bent to the desired angle. The method is not only time-consuming, but also involves the problem that the workpiece must be gripped by the bending machine at exactly the same point in order to be reworked correctly, which results in an additional potential source of error for the correction bend.

Modern fully automatic machines for precise bending or bending of sheet metal often have one or more integrated angle measuring devices, with the help of which the angle obtained is automatically determined after the bending process, in which case one or more subsequent correction bends are carried out if the deviations from the target value are too great. This procedure is complex in terms of equipment and expensive and, above all, limits the machine capacity, particularly if, for example, in the event of dimensional inaccuracies due to fluctuating sheet quality, additional correction bending processes have to be initiated which take up the corresponding machine time.

All current systems have the disadvantage that the control measurement takes place during the folding process, in which case the folding machine is blocked, so that machine time for production is lost and the machine capacity is limited.

The object of the present invention is to provide a method for bending or bending sheet metal with precise angles, which has advantages over the prior art. The object of the present invention is also a device to provide for carrying out the method according to the invention.

The object is achieved by a method having the features of claim 1 and an apparatus having the features of claim 12. Advantageous refinements and developments of the present invention are the subject of the corresponding subclaims.

The invention is based on the knowledge that angular inaccuracies when bending or bending sheet metal are mostly due to the fluctuating sheet quality. It was found that the dimensional accuracy of the specified sheet type and rolling direction depends largely on the thickness of the sheet and that the angular deviation correlates with the weight of the sheet or the thickness of the sheet.

From this it was concluded that by weighing the sheet before folding or bending, then measuring and, if necessary, subsequently correcting the bending angle, data can be collected on a few freely selected comparison sheets, with the aid of which the machine can be set up or programmed so that the machine parameters adjust automatically in the ongoing series process in correlation to the weight of the sheet to be processed, so that exact angles can be achieved without additional correction bends if the weight of the sheet to be processed was determined before the bending process.

This procedure is significantly less complex than the previously known correction methods and has the additional advantage that machine capacity is gained, since after setting or programming the machines to a defined one Forming process with a correction factor or correction program determined on the basis of a few sheets, in which the relation of the weight of the sheet to the bending angle achieved is essentially no longer necessary to carry out additional correction steps in order not only to obtain the desired angular accuracy, but also within a series production to guarantee. As with any larger production series, only the occasional control measurements that are customary for reasons of quality assurance are then to be carried out, the frequency of which drastically decreases in the course of a production series, in particular in the method according to the invention, in which additional quality assurance is achieved by the upstream weight measurement. Ideally, the control measurements in the course of a production series are superfluous.

In addition to the weight, the rolling direction of the sheet also influences the bending angle, so that the correction method described above has to be initiated again if the rolling direction of the sheet to be processed changes. In practice, you can help yourself by processing sheet metal series with different rolling directions separately. In the simplest case, the machine operator separates sheet metal series with different rolling directions before the production series, which can be optically identified on the basis of their rolling tracks.

The process for bending or bending sheet metal with precise angles is carried out on a conventional CNC-controlled machine for sheet metal processing, with the first step being to weigh a first sheet to be processed before bending or bending. The sheet is then bent or bent using specified machine parameters. Then the bending angle is determined and the The value found for the bending angle is entered into the control program of the machine together with the specified machine parameters, the weight of the sheet and, if applicable, the rolling direction of the sheet in relation to a predetermined bending angle, or is adopted by the latter in order to determine corrected machine parameters for a corrective bending. These steps are preferably carried out with at least one further sheet, which ideally should have a different weight.

On the basis of the measured bending angle, a correction factor or a correction program for the bending or bending process is now determined depending on the weights of the respective sheets, the difference between the measured actual bending angle and the predetermined bending angle being used to calculate the deformation path for a subsequent bending process in one Series production is the basis. As soon as the correction factor or the correction program has been determined, the series production of folded or bent sheet metal parts can take place, the sheets to be processed always being weighed first and then bent or bent using the corrected correction factor or correction program.

The method according to the invention is particularly suitable for the so-called free bending of metal sheets, the bending angle being formed by the die inlet edges and the tip of the folding punch. The depth of insertion of the punch tip into the die determines the bending angle. The bending angle is corrected by changing the immersion depth of the punch tip into the die. The particular advantage of free bending can be seen in the fact that any bending angle can be bent with a tool set. A disadvantage of free bending consists in the lack of precision due to sheet metal tolerances, but this can now be largely compensated for by the method according to the invention.

In an advantageous embodiment of the method according to the invention, it is provided that after the angle measurement of the comparison sheets and the subsequent determination of the machine parameters for a correction bend, a corresponding correction bend is also carried out and the bending angles determined during the correction bend together with the machine parameters set during the correction bend are also used to determine the Correction factor or correction program can be used.

The particular advantage of the method is based on the fact that the control measurements of the angles, which are frequently to be carried out in series production for reasons of quality assurance, are superfluous. It was found that the machine parameters can be set automatically with the aid of previously determined correction factors in such a way that the bending angles obtained in a first operation are within the specified tolerance for the desired value with a high degree of certainty. To increase process reliability, random control measurements of the bending angle can also be carried out.

The measurement of the bending angle itself can be done with the usual measuring devices. In the simplest case, a conventional manually operated protractor can be used.

Of course, according to a less personnel-intensive embodiment of the present method, the angle measurement can be integrated into the bending machine or be carried out with it combined measuring systems, whereby the angle measurement can be carried out with the aid of an optical measuring beam, via distance sensors or with the aid of laser-supported bending angle measuring devices. It should be noted, however, that integrated angle measuring devices are relatively expensive and the number of angle measurements required for quality assurance is drastically reduced precisely by the method according to the invention, so that such a combination is more suitable for special cases.

The values and machine parameters determined in the preliminary tests are preferably entered into or adopted by a control program for a fully automatic bending system, and the correction factor or correction program is determined via the control program, the control program advantageously being part of the machine control of the CNC-controlled machine for sheet metal processing is.

The advantages of the method according to the invention are particularly evident when a scale is integrated in the CNC-controlled machine for sheet metal processing, which is directly connected to the control program and communicates with it. For fully automatic processing of sheets, it is advisable to arrange the scale in the area of the sheet feed, which can then be done, for example, using a robot equipped with an integrated scale.

The present invention also relates to a device for bending or bending sheet metal with precise angles, the device being a conventional CNC-controlled machine for sheet metal processing, which comprises a control program for controlling the machine, which is able to use data of comparative weight - and angle measurements on at least to determine a correction factor or a correction program for a sheet to be machined for an angularly accurate bending or bending of sheets for series production.

A preferred embodiment of the device for bending or bending sheet metal with precise angles provides that the device comprises a scale which is connected to the control program for controlling the machine and communicates directly with it. After the weight of the sheet has been recorded, the sheet is bent and the bending angle obtained is preferably determined manually using an angle measuring device. The correction factor is determined based on the weight of the sheet and the bending angle achieved. Several sheets can be measured to determine the correction factor. After the correction factor has been determined, no further angle measurements are required, and series production can take place, in which case angle measurements can only be carried out at random for quality assurance reasons.

The device can optionally additionally comprise an angle measuring device which, together with the scale, is connected to the control program for controlling the machine and communicates with it. The control program is then able to determine a correction factor or a correction program for series production on the basis of comparative weight and angle measurements on sheets which preferably have at least two different weights.

At this point it should be pointed out again that not only the weight, but also the direction of rolling of the sheet has an influence on the bending angle. Before starting a production series, the sheets to be bent have to be bent sorted according to their rolling direction. This sorting is conveniently done after cutting the sheets. The corresponding correction factors and correction programs must be determined separately for sheets in different rolling directions. This sorting is usually carried out by the machine operator, since automatic optical detection of the sheets with different rolling directions has not yet been possible.

The present invention is explained in more detail below with reference to a drawing and examples.

The Figure 1 shows a sectional view of a schematic representation of the free bending, in which the bending angle of the sheet 3 is formed by the leading edges 4 of the die 2 and the tip of the folding punch 1.

The following examples relate to free bending.

example 1

Cladding parts made of sheet steel were folded using a CNC-controlled hydraulic press brake with a press force of 500 to 10,000 kN. The specified square angle was 90 °. The sheet had a thickness of approx. 3 mm. In free bending, using sheets with the same rolling direction, the bending angles listed in the following table were determined: Table 1 workpiece Weight (g) Angle (°) Sheet 1 200 90 Sheet 2 195 91 Sheet 3 215 87

On the basis of the results of the weight and angle measurements listed in the table above and the determined difference between the actual value and the setpoint of the bending angle depending on the weight of the sheet, a correction factor can be determined so that the different sheet thicknesses and the specific sheet thicknesses can be bent or bent over expected springback can be compensated. In this simple example, an angle correction of 1 ° is required for every 5 g of weight. As part of the correction, the path of the folding stamp is adapted to the sheet thickness. With higher weight (= thicker sheet), the path must be reduced in order to reach the target angle.

Examples 2 to 5

Table 2 below summarizes further examples which were processed under the same conditions. Table 2 example Material strength Sheet 1 Sheet 2 Sheet 3 Weight angle Weight angle Weight angle 2nd VA sheet 3 mm 1050 g 90 ° 1040 g 90, 3 ° 1070 g 89 ° 3rd Aluminum sheet 2 mm 265 g 90 ° 255 g 93 ° - - 4th VA sheet 1 mm 50 g 90 ° 48 g 91 ° - - 5 Sheet steel 4 mm 950 g 90 ° 920 g 92 ° 960 g 89 °

The specified edge angle was again 90 °.

The correction factor can be determined on the basis of the results of the weight and angle measurements listed in the table above and the difference between the actual value and the setpoint of the bending angle as a function of the weight of the sheet, so that the different sheet thicknesses and the different sheet thicknesses can be bent or bent over expected springback can be compensated.

In this context it should be noted that simple examples were deliberately chosen to illustrate the inventive idea. The idea of the invention naturally also encompasses applications in which the machine is controlled with the aid of further parameters and the determination of a correction factor or correction program is considerably more complicated. Applications are also considered, the results of force measurements being included in the calculation of the deformation path for a final bending process, for example if the springback is also measured using force measuring devices, or applications in which, for example, the feed stroke, the pressing force and the speed are dependent can be varied from the measured sheet weights and bending angles to determine the correction factor or correction program in order to enable an angle-accurate bending or bending.

Claims (15)

1. A method for angle-precise folding or bending of sheet metals (3), wherein the folding or bending operation is carried out on a conventional CNC-controlled machine for sheet metal working, comprising the steps:

   a) weighing at least one first sheet metal (3) to be processed,

   b) folding or bending the sheet metal (3) using prespecified machine parameters,

   c) determining the bending angle,

   d) entering or taking over the value found for the bending angle together with the prespecified machine parameters and the weight of the sheet metal (3) in relation to a prespecified bending angle into a control program for determining corrected machine parameters for a correction bending,

   e) determining a correction factor and/or a correction program for the folding or bending operation using the measured bending angles in dependence of the weights of the respective sheet metals (3), wherein the difference between the measured actual bending angle and the prespecified bending angle is used as the basis for calculating the deformation path for a subsequent bending operation in a series production,

   f) series production of folded or bent sheet metal parts, wherein the sheet metals (3) to be processed are first weighed and then folded or bent using the correction factor and/or correction program determined.
2. The method according to claim 1, characterized in that after step d), steps a) to d) are repeated with a further sheet metal (3) in an additional step.
3. The method according to claim 2, characterized in that the at least one further sheet metal (3) has a different weight.
4. The method according to claim 1, characterized in that after step d), a correction bending is performed and the bending angle determined at the correction bending is used together with the machine parameters set at the correction bending to determine corrected machine parameters for a correction bending.
5. The method according to one of claims 1 to 4, characterized in that the measurement of the bending angle is carried out with the aid of a manually operated conventional protractor, with the aid of an optical measuring beam, via distance sensors or with the aid of laser-supported bending angle measuring devices.
6. The method according to one of claims 1 to 4, characterized in that the measurement of the bending angle is carried out with the aid of a measuring system integrated in the bending machine or combined with the bending machine, wherein the angle measurement is carried out with the aid of an optical measuring beam, via distance sensors or with the aid of laser-supported bending angle measuring devices.
7. The method according to one of claims 1 to 4, characterized in that the values and machine parameters determined in steps c) to e) are entered into a control program for a fully automated bending system or taken over from it and the determination of the correction factor and/or correction program is carried out via the control program.
8. The method according to one of claims 1 to 7, characterized in that the control program is a part of the machine controller of the CNC-controlled machine for sheet metal working.
9. The method according to claim 8, characterized in that a scale, which is connected to and communicates with the control program, is integrated in the CNC-controlled machine for sheet metal working.
10. The method according to claim 9, characterized in that an angle measuring device, which - together with the scale - is connected to the control program and communicates with it, is additionally integrated in the CNC-controlled machine for sheet metal working.
11. The method according to one of claims 1 to 10, characterized in that the CNC-controlled machine for sheet metal working is part of a fully automated plant for sheet metal working, wherein the plant comprises a robot for feeding the sheet metal parts to be processed, wherein a scale for weighing the sheet metal parts is integrated in the robot, said scale being connected to the control program of the CNC-controlled machine and communicating with it.
12. A device for angle-precise folding or bending of sheet metals, wherein the device comprises a conventional CNC-controlled machine for sheet metal working, characterized in that the CNC-controlled machine for sheet metal working comprises a control program for controlling the machine, wherein the control program determines a correction factor and/or a correction program for angle-precise folding or bending of sheet metals (3) for series production on the basis of data from comparative weight and angle measurements on at least one sheet metal (3) to be processed.
13. The device according to claim 12, characterized in that the device comprises a scale for weighing the sheet metals (3) to be processed, wherein the scale is connected to and directly communicates with the control program for controlling the machine.
14. The device according to claim 12 or 13, characterized in that the device comprises an angle measuring device, wherein the angle measuring device is connected to and directly communicates with the control program for controlling the machine.
15. The device according to one of claims 12 to 14, characterized in that the device comprises a force measuring device, wherein the force measuring device is connected to and directly communicates with the control program for controlling the machine.

Images